Electron-gun assembly for cathode-ray signal-storage tubes



April 28, 1964 R. J. MADDEN ETAL 3,131,324

ELEcTRoN-GUN ASSEMBLY FOR cATHoDE-RAY SIGNAL-STORAGE TUBES Filled Nov. 13, 1961 I7 is 2o I9 FIG-1 +2oov+` United States Patent O 3,131,324 ELECTRGN-GUN ASSEMBLY FR CATHODE-RAY SIGNAL-STGRAGE TUBES Robert l. Madden, Bioomdeld, and Victor Le Gendre,

Wayne, NJ., assignors to Fairchild Carrera and instinment Corporation, a corporation of Delaware Filed Nov. 13, 1961, Ser. No. 151,879

4 Claims. (Cl. 313-82) rl`his invention relates to electron-gun assemblies for cathode-ray signal-storage tubes Iand particularly for such storage tubes of the direct-view type having electrostatic deiiection plates in which electron coupling between the viewing gun electrodes and the deection plates is substantially eliminated.

Direct-view cathode-ray storage tubes have found extensive use in -a number of lields, particularly as rad-ar display devices, since they combine the features of signal storage and signal display in a single tube. A typical direct-view storage tube of this type includes a writing gun assembly, a flood-gun assembly, deflection plates for the writing gun, a storage or target grid assembly, and a liuorescent display screen.

The Iwriting gun assembly produces a sharply focused beam which may or may not be modulated by a signal input and deflected to scan the target grid and lay down a charge pattern on it representative of the signal input. The ilood-gun :assembly develops `a low-voltage, wide angle electron beam or stream which iioods the target storage grid. Electrons trom this latter beam are attracted to the liuorescent screen, the intensity at each elemental area being modulated by the intensi-ty of the charge pattern of .a corresponding elemental area of the storage grid.

There results a bright display of the input signal which may be either of the light-trace .or dark-trace type, depending on the accelerating voltage applied to the scanning beam. For example, if the input signal is a periodic Wave -to be analyzed, it is applied to one of the set of deflection pl-ates rather than to Ia modulating electrode and its |wave form appears `as a light line on a dark background, as in the `conventional cathode-ray oscilloscope, or a dark line on a light background. [The latter type of display corresponds more `closely to usual graph-ical representations and it has been found .that it can be interpreted by the operator with greater accuracy and tacility.

In a typical prior cathode-ray signal-storage tube of the type described, the deflection plate shield has been used to -support and connect together both the pre-accelerator and accelerator of the writing gun and the accelerator of the ood gun. As a consequence, the deection plates have been in relatively close proximity to, and exposed to, the densely collimated nood-gun stream comprising both .the primary -and reflected electrons. As a result, the deilection plates, during the peak portions of their scanning potential waves, may :assume a substantially positive potential relative to the flood-gun stream and attract an appreciable portion of .the Hood-gun current, either that of the .primary flood-gun stream or the returning secondary electron stream. Such a ilow of current in the deection plate circuits constitutes -a dynamic loading .of the circuits which may impair the deflection linearity or the fidelity of representation of the input signal, or both, which obviously is undesirable.

It is an object of the invention, therefore, to provide a new and improved electron-gun assembly for a cathoderay signal-storage tube which obviates the yforegoing lim-itations of prior storage tubes of the type described.

It is 'another lobject of the invention to provide a ice new and improved electron-gun assembly tor a cathoderay signal-storage tube in which the deliection plates effectively are isolated `from the flood-gun electron stream.

It is a further object of the invention to provide a new and improved electron-gun assembly for a cathode-ray signal-storage tube in lwhich the writing gun system and the flood-gun system, between Iwhich a high potential gradient exists, are electrically shielded from each other.

In accordance with the invention, an electron-gun assembly `for a cathode-ray signal-storage tube including electrostatic dellection plates and a signal-storage grid comprises a writing gun yfor scanning the storage grid including an electron-beam source and a iirst accelerating electrode member relatively positioned to be disposed on opposite sides axially of the deilection plates, such electrode member being dimensioned eiiectively to shield the ldeiiection plates from all axially following tube elements, and a iiood gun for flooding the storage grid including an electron-beam source positioned axially approximately coincidently with the iirst accelerating electrode member and a second accelerating electrode member positioned axially beyond the irst accelerating electrode member, whereby the deilection plates yare electrically shielded lfrom the ilood-gun beam.

For a better understanding of the present invention, together with other and further object-s thereof, reference is had to the following `description while its scope will be pointed out in the appended claims.

`Referring now to the drawing:

FIG. l is a simplified representation of a cathode-ray signal-storage tube including ian electron-gun assembly embodying the invention, while FIG. 2 is a schematic representation of the apparatus of FIG. 1.

Referring nofw more particularly to FIG. 1 of the drawing, there lis represented an electron-gun assembly for a cathode-ray signal-storage tube lll including two pairs of deflection plates 12, `12 and 13, 13, which may be conventional, a signal-storage grid 14, an elongated enclosing envelope 11, and a liu-crescent screen 15 deposited on the 4face of the envelope 11 having a conductive metallic coating 16. The storage grid 14 is shown greatly enlarged for the sake of clarity and may comprise a wire mesh having a nonconductive coating 14a facing the iiood gun and consisting of a dielectric material such as magnesium uoride or silicon monoxide. Adjacent the storage grid 14 is la collector electrode 9, usually in the form of la wire screen or mesh, `for collecting secondary electrons emitted by the target 14.

The electron-gun assembly of the invention comprises a writing gun for scanning the storage grid 14 including an electron-beam source, such as a cathode and grid-cup unit 17, iirst and second anodes or accelerating electrodes 18 and 19, and a focusing electrode 20 interposed therebetween. The writing gun assembly further includes an accelerating electrode 21 positioned relative to the gridcathode unit 17 so as to be disposed on opposite sides axially of the deflection plates 12, 12, 13, 13. While the detailed construction of this writing gun assembly is not shown since it may be conventional, the accelerating electrode 21 preferably comprises a conductive disc extending substantially across the envelope 11 and serves as a supporting member for the gun comprising the elements 17, 18, 19, 20. With such an arrangement, the electrode 21 effectively shields the deflection plates 12, 13 electrically from all axially following tube elements.

The electron-gun assembly of the invention further includes a llood gun for ilooding the storage grid 14, this gun including an electron-beam source, such as a gridcathode unit 22, which is positioned axially approximately coincidently with the accelerating electrode 21 but electrically insulated therefrom.

The ood-gun assembly further comprises an accelerating electrode member 23 positioned axially beyond the accelerating electrode 21. The ood-gun electrode elements may be physically supported by either the writing gun accelerator disc 21 or the ood-gun accelerator 23 but are electrically insulated from both. The accelerating electrode 23 may be in the form of a conductive disc similar to the electrode 21 and these electrodes are provided with rectangular apertures or windows 21a, 22a, respectively, which are in axial alignment and dimensioned to pass the writing gun beam through its range of deflection under the inuence of the deflection plates 12, 12 and 13, 13.

It is believed that the operation of the electron-gun assembly will be apparent from the foregoing description. By way of illustration, it may be assumed that the tube of FIG. l is of the type 8124. The operating potentials indicated as applied to the several electrodes of the writing gun and the flood gun are illustrative only, assuming that the tube is to be operated as a light-trace tube and it being understood that they may be adjusted in accordance with well-known principles for particular tube types and particular applications to reduce current in the circuits of the deflection plates substantially to zero. Under these conditions, it will be assumed that initially no signal is applied to the grid-cathode unit 17, in which case the flood gun comprising elements 22, 23 will flood the storage grid 14 with a low-voltage beam so that the dielectric coating 14a is uniformly charged approximately to the potential of the flood-gun cathode, that is, 0 volts. Under these no-signal conditions, the major portion of the flood-gun electron stream will pass through the storage grid 14 and the face of the tube will be uniformly bright although, under normal conditions, the face of the tube will be dark.

If, now, a signal is applied to the grid-cathode unit 17 and a signal to be analyzed is applied to the one set of deliection electrodes, for example the electrodes 12, 12, the writing gun, in conjunction with the deflection plates 12, 12, 13, 13, will scan the storage grid 14. The voltage of the writing beam is made sufficiently high that it strikes the storage grid 14 above the first cross-over point but below the second cross-over point on the secondary emission ratio curve for the particular insulating coating 14a. Above this first cross-over point, the secondary emission ratio is greater than unity, the secondary electrons being drawn off by the collector 9. As a result, at those points of the storage grid scanned by the writing beam, the local elemental areas of the storage grid are charged positively so that, in these local areas, the low-voltage electrons of the flood gun are permitted to penetrate the storage grid 14. Thus, the corresponding areas of the iiuorescent screen 16 are bright but the remaining portions of the storage grid assume a negative charge so that there is formed the conventional light trace on a dark background.

With the arrangement described, it is seen that the deflection plates 12, 12, 13, 13 are effectively shielded from the flood-gun electron stream by the accelerating electrode 21 of the writing gun. As a result, the deflection plates 12, 12 and 13, 13 cannot draw electron current from the dood-gun stream, thus avoiding loading of the deection plate circuits and the consequent impairment of the deflection linearity and of the fidelity of representation of the input signal.

FIG. 2 is a schematic representation of the apparatus of FIG. 1 in which it is seen that the writing gun is a conventional S-electrode assembly including a control grid 24 while the flood gun is of a conventional triode configuration including a control grid 25. Furthermore, the flood gun operates somewhat analogously to a conventional triode in which the storage grid 14 acts as a control grid to provide image amplification. At the same time, as is typical of direct-view storage tubes, the display can be extremely bright, adequate for daylight viewing, due to the duty cycle of the flood gun. The electron stream of this gun may be of the order of a feW milliamperes while the beam current of the writing gun may be only a few hundred microamperes.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. An electron-gun assembly for a cathode-ray signalstorage tube including electrostatic deflection plates and a signal-storage grid comprising: a writing gun for scanning said grid including an electron-beam source and a first accelerating electrode member relatively positioned to be disposed on opposite sides axially of the deflection plates, said accelerating electrode member being dimensioned effectively to shield the defiection plates from all axially following tube elements; and a iiood gun for flooding said grid including an electron-beam source positioned axially approximately coincidently with said accelerating electrode member and a second accelerating electrode member positioned axially beyond said irst accelerating electrode member, whereby the deiiection plates are electrically shielded from the flood-gun beam.

2. An electron-gun assembly for a cathode-ray signalstorage tube including electrostatic deflection plates and a signal-storage grid comprising: a writing gun for scanning said grid including an electron-beam source and a first accelerating electrode member relatively positioned to be disposed on opposite sides axially of the deflection plates, said accelerating electrode member serving as a gun-supporting member and being dimensioned effectively to shield the deflection plates from all axially following tube elements; and a flood gun for flooding said grid including an electron-beam source positioned axially approximately coincidently with said accelerating electrode member and a second accelerating electrode member positioned axially beyond said first accelerating electrode member and serving as a gun-supporting member, whereby the deflection plates are electrically shielded from the flood-gun beam.

3. An electron-gun assembly for a cathode-ray signalstorage tube including electrostatic deflection plates, a signal-storage grid, and an elongated enclosing envelope comprising: a writing gun for scanning said grid including an electron-beam source and a first accelerating electrode member relatively positioned to be disposed on opposite sides axially of the deflection plates, said accelerating electrode member comprising a conductive disc extending substantially across the envelope effectively to shield the deflection plates from all axially following tube elements; and a fiood gun for flooding said grid including an electron-beam source positioned axially approximately coincidently with said accelerating electrode member and a second accelerating electrode member positioned axially beyond said first accelerating electrode member, whereby the deflection plates are electrically shielded from the flood-gun beam.

4. An electron-gun assembly for a cathode-ray signalstorage tube including electrostatic 'deflection plates, a 'signal-storage grid, and an elongated enclosing envelope comprising: a Writing gun for scanning said grid including an electron-beam source and a first'acceleratingelectrode member relatively positioned to be disposed on opposite sides axially ofthe defiection plates, said accelerating electrode member comprising a conductive disc extending substantially across the envelope effectively to shield the deiiection plates from all axially following tube elements; and a flood gm for iiooding said grid including an electron-beam source positioned axially approximately coincidently with said accelerating electrode member and a second accelerating electrode member positioned axially beyond said first accelerating electrode member and comprising a conductive disc extending substantially across the envelope, said conductive discs having aligned apertures dimensioned to pass the writing gun beam throughout its range of deflection, whereby the deection paltes are electrically shielded from the flood-gun beam.

References Cited in the le of this patent UNITED STATES PATENTS Liebmann Aug. 12, 1947 Jensen June 3, 1952 Beintema May 29, 1956 Davis Oct. 1, 1957 Stone Feb. 10, 1959 

1. AN ELECTRON-GUN ASSEMBLY FOR A CATHODE-RAY SIGNALSTORAGE TUBE INCLUDING ELECTROSTATIC DEFLECTION PLATES AND A SIGNAL-STORAGE GRID COMPRISING; A WRITING GUN FOR SCANNING SAID GRID INCLUDING AN ELECTRON-BEAM SOURCE AND A FIRST ACCELERATING ELECTRODE MEMBER RELATIVELY POSITIONED TO BE DISPOSED ON OPPOSITE SIDES AXIALLY OF THE DEFLECTION PLATES, SAID ACCELERATING ELECTRODE MEMBER BEING DIMENSIONED EFFECTIVELY TO SHIELD THE DEFLECTION PLATES FROM ALL AXIALLY FOLLOWING TUBE ELEMENTS; AND A FLOOD GUN FOR FLOODING SAID GRID INCLUDING AN ELECTRON-BEAM SOURCE POSITIONED AXIALLY APPROXIMATELY COINCINDENTLY WITH SAID ACCELERATING ELECTRODE MEMBER AND A SECOND ACCELERATING ELECTRODE MEMBER POSITIONED AXIALLY BEYOND SAID FIRST ACCELERATING ELECTRODE MEMBER, WHEREBY THE DEFLECTION PLATES ARE ELECTRICALLY SHIELDED FROM THE FLOOD-GUN BEAM. 